Method for producing ink-jet head and ink-jet head

ABSTRACT

A method for producing an ink-jet head includes forming a buffer layer on an upper surface of a vibration plate, and forming a piezoelectric precursor layer on an entire upper surface of a surface layer, the piezoelectric precursor layer being converted into a piezoelectric sheet. The buffer layer is formed of a material with which mutual diffusion between the piezoelectric precursor layer and the buffer layer is hardly caused as compared with mutual diffusion between the piezoelectric precursor layer and the vibration plate with which no buffer layer is provided. A stack, in which the buffer layer and the piezoelectric precursor layer are formed, is heated at a predetermined temperature, and the piezoelectric precursor layer is calcinated to form the piezoelectric sheet. It is possible to suppress the deterioration of the performance of the piezoelectric member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for producing an ink-jet headfor discharging an ink onto a recording medium. The present inventionalso relates to the ink-jet head.

2. Description of the Related Art

Japanese Patent Application Laid-open No. 11-334087 (FIG. 1) describes amethod for producing an ink-jet head including a vibration plate and apiezoelectric film formed on the vibration plate wherein the vibrationplate is continuously formed on a substrate arranged with a plurality ofpressure chambers to have such a size that all of the pressure chambersare covered with the vibration plate, the vibration plate and thepiezoelectric film being composed of metal materials having coefficientsof thermal expansion similar to one another. According to thismethod,.when the piezoelectric film is formed on the vibration plate, astack or laminate, which is composed of the vibration plate and thepiezoelectric film, is suppressed from causing any warpage which wouldbe otherwise caused by the difference between the coefficients ofthermal expansion of the vibration plate and the piezoelectric film.

However, in the case of the method for producing the ink-jet headdescribed in Japanese Patent Application Laid-open No. 11-334087, anymutual diffusion occurs between the materials for constructing thevibration plate and the piezoelectric film, and the crystal growth ofthe piezoelectric film is inhibited during the calcination of thepiezoelectric film, when the piezoelectric film is thermally formed orcalcinated on the vibration plate. As a result, the performance of thepiezoelectric film is deteriorated.

SUMMARY OF THE INVENTION

In view of the above, an object of the present invention is to provide amethod for producing an ink-jet head and the ink-jet head which suppressthe deterioration of the performance of a piezoelectric member.

According to a first aspect of the present invention, there is provideda method for producing an ink-jet head, comprising the steps of:

manufacturing a flow passage unit including a vibration plate which ismade of metal, an ink chamber which is closed by the vibration plate,and a nozzle which is communicated with the ink chamber and whichdischarges an ink;

forming a first buffer layer on the vibration plate;

forming a piezoelectric precursor on the first buffer layer; and

heating the flow passage unit, the first buffer layer, and thepiezoelectric precursor so that the piezoelectric precursor iscalcinated into a piezoelectric member, wherein:

the first buffer layer is formed of a metal material with which mutualdiffusion between the first buffer layer and the piezoelectric precursorduring the heating is less than mutual diffusion between thepiezoelectric precursor and the vibration plate when the heating isperformed without the first buffer layer.

Accordingly, the first buffer layer, which is composed of the metalmaterial with which the mutual diffusion of the material with respect tothe piezoelectric precursor is hardly caused as compared with thevibration plate, is allowed to intervene between the piezoelectricprecursor and the vibration plate. Therefore, the mutual diffusion ishardly caused between the material for constructing the piezoelectricprecursor and the material for constructing the vibration plate duringthe heating step. As a result, the crystal growth of the piezoelectricprecursor is easily advanced in the heating step, and the performance ofthe piezoelectric member to be obtained is hardly deteriorated.

In the present invention, the method for producing the ink-jet head mayfurther comprise, before the heating step, a step of forming, on thefirst buffer layer, a second buffer layer formed of a metal materialwith which mutual diffusion between the second buffer layer and thepiezoelectric precursor during the heating is less than the mutualdiffusion between the vibration plate and the piezoelectric precursorwhen the heating is performed without the second buffer layer.Accordingly, the mutual diffusion is effectively prevented in theheating step between the material for constructing the piezoelectricprecursor and the material for constructing the vibration plate.

In the present invention, it is also preferable that the second bufferlayer may have oxidation resistance which is equivalent to or greaterthan that of the vibration plate. Accordingly, any oxide film is hardlyformed between the second buffer layer and the piezoelectric precursorin the heating step, because the second buffer layer is excellent in theoxidation resistance. Therefore, it is possible to apply a sufficientelectric field to the piezoelectric member and the vibration plate.

In the present invention, the vibration plate may be formed of any oneof materials of stainless steel, titanium, and 42 Alloy, and the heatingmay be performed in the heating step at a temperature of 600° C. to 900°C. Accordingly, the metal, which constitutes the vibration plate, hardlycauses the decrease in the strength.

In the present invention, the first buffer layer may be formed ofnickel. Nickel is cheap, and hence it is possible to decrease theproduction cost of the ink-jet head.

In the present invention, the second buffer layer may be formed of gold.Gold has the excellent oxidation resistance and the excellent thermalstability. Therefore, the mutual diffusion is hardly caused between thepiezoelectric precursor and the vibration plate in the heating step.Further, any oxide film is hardly formed between the second buffer layerand the piezoelectric precursor.

According to a second aspect of the present invention, there is provideda method for producing an ink-jet head, comprising the steps of:

manufacturing a flow passage unit including a vibration plate which ismade of metal, an ink chamber which is closed by the vibration plate,and a nozzle which is communicated with the ink chamber and whichdischarges an ink;

forming a nickel layer on the vibration plate;

forming a gold layer on the nickel layer;

forming a piezoelectric precursor on the gold layer; and

heating the flow passage unit, the nickel layer, the gold layer, and thepiezoelectric precursor at a temperature of 600° C. to 900° C. so thatthe piezoelectric precursor is calcinated into a piezoelectric member.Accordingly, the nickel layer and the gold layer intervene between thevibration plate and the piezoelectric member. Gold has the excellentoxidation resistance and the excellent thermal stability. Nickel hassuch a property that it hardly inhibits the crystal growth of thepiezoelectric precursor. Therefore, the mutual diffusion is hardlycaused between the piezoelectric precursor and the vibration plate as awhole in the heating step. Further, any oxide film is hardly formed withrespect to the piezoelectric precursor. As a result, the crystallizationof the piezoelectric precursor is advanced, and the performance of thepiezoelectric member is hardly deteriorated. Further, nickel is cheap,and hence it is possible to decrease the production cost of the ink-jethead.

According to a third aspect of the present invention, there is providedan ink-jet head comprising:

a flow passage unit which includes a vibration plate made of metal, anink chamber closed by the vibration plate, and a nozzle communicatedwith the ink chamber to discharge an ink;

a first buffer layer which is formed on the vibration plate; and

a piezoelectric member which is formed on the first buffer layer andwhich is obtained by calcinating a piezoelectric precursor, wherein:

the first buffer layer is formed of a metal material with which mutualdiffusion between the piezoelectric precursor and the first buffer layerduring heating for the calcination is less than mutual diffusion betweenthe piezoelectric precursor and the vibration plate when the heating isperformed without the first buffer layer. Accordingly, the first bufferlayer, which is composed of such a metal material that the mutualdiffusion of the material with respect to the piezoelectric precursor ishardly caused as compared with the vibration plate, is allowed tointervene between the piezoelectric precursor and the vibration plate.Therefore, the head is provided, in which the mutual diffusion is hardlycaused between the material for constructing the piezoelectric precursorand the material for constructing the vibration plate. Thus, the head isprovided, in which the decrease in the piezoelectric characteristic ofthe piezoelectric member is suppressed.

In the present invention, the ink-jet head may further comprise a secondbuffer layer which is formed between the first buffer layer and thepiezoelectric member and which is formed of a metal material with whichmutual diffusion between the second buffer layer and the piezoelectricprecursor during the heating is less than the mutual diffusion betweenthe vibration plate and the piezoelectric precursor when the heating isperformed without the second buffer layer. Accordingly, the mutualdiffusion between the material for constructing the piezoelectricprecursor and the material for constructing the vibration plate iseffectively prevented. The head is provided, in which thecrystallization of the piezoelectric precursor is further advanced.

In the present invention, the second buffer layer may have oxidationresistance which is equivalent to or greater than that of the vibrationplate. Accordingly, any oxide film is hardly formed between the secondbuffer layer and the piezoelectric precursor. Therefore, it is possibleto apply a sufficient electric field to the piezoelectric member and thevibration plate.

According to still another aspect of the present invention, there isprovided an ink-jet printer comprising the ink-jet head according to thethird aspect of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view illustrating a schematic arrangement ofan ink-jet printer including an ink-jet head according to an embodimentof the present invention.

FIG. 2 shows a plan view illustrating a head main body shown in FIG. 1.

FIG. 3 shows a partial sectional view taken along a line III-III shownin FIG. 2.

FIG. 4 shows a magnified view illustrating an area surrounded by dashedlines depicted in FIG. 3.

FIG. 5 shows steps of producing the ink-jet head.

FIGS. 6A to 6D show parts of the steps of producing the ink-jet headaccording to the embodiment of the present invention, wherein FIG. 6Ashows a situation in which a stack is formed by four plates except for anozzle plate, FIG. 6B shows a situation in which a first buffer layer isformed on an upper surface of an actuator plate and a second bufferlayer is formed on the first buffer layer, FIG. 6C shows a situation inwhich a piezoelectric sheet is formed on the second buffer layer, andFIG. 6D shows a situation in which an individual electrode is formed onthe piezoelectric sheet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention will be explained belowwith reference to the drawings.

FIG. 1 shows a perspective view illustrating a schematic arrangement ofan ink-jet printer including an ink-jet head according to an embodimentof the present invention. As shown in FIG. 1, the ink-jet printer 1comprises a platen roller 40 which transports the printing paper 41 as arecording medium, an ink-jet head 9 which discharges an ink onto theprinting paper 41 set on the platen roller 40, and a flexible printedcircuit (FPC) 20 which supplies a driving voltage from a control unit(not shown) to the ink-jet head 9.

The platen roller 40 is rotatably attached to a frame 43 by the aid of ashaft 42, and is driven and rotated by a motor 44. The printing paper 41is fed from a paper feed cassette (not shown) which is provided in thevicinity of the ink-jet printer 1. The printing paper 41 is transportedat a constant speed in the direction of the arrow shown in the drawingby the aid of the platen roller 40. Predetermined printing operation isperformed with the ink discharged from the ink-jet head 9. After that,the printing paper 41 is discharged. Detailed illustrations of a paperfeed mechanism and a paper discharge mechanism for the printing paper 41are omitted from FIG. 1. The ink-jet printer 1, which is depicted inFIG. 1, is a monochrome or black and white printer in which only oneink-jet head 9 is arranged. However, when the color printing isperformed, at least four ink-jet heads 9 of yellow, magenta, cyan, andblack are arranged in parallel.

As appreciated from FIG. 1, the ink-jet head 9 is a line head whichextends perpendicularly to the transport direction of the printing paper41, and it is installed and fixed to the frame 43. The ink-jet head 9 isprovided to discharge the ink onto the printing paper 41. The ink-jethead 9 has a head main body 100 and a base section 11. The head mainbody 100 extends in a form of line in one direction (directionperpendicular to the transport direction of the printing paper). Thebase section 11 extends in a direction perpendicular to the head mainbody 100, and it supports the head main body 100.

An ink discharge surface of the head main body 100, which is the bottomsurface of the ink-jet head 9 and on which a large number of nozzles 8(see FIG. 3) are formed in an array in the longitudinal direction, isopposed in parallel to the transport surface of the printing paper 41 tobe transported by the platen roller 40. Therefore, when the drivingvoltage is supplied from the control unit via FPC 20 to the head mainbody 100, the ink, which is discharged from the respective nozzles 8formed on the ink discharge surface of the head main body 100, fliestoward the printing paper 41. FPC 20 is electrically connected to apiezoelectric sheet 21 at the upper surface of the head main body 100 asdescribed later on.

Next, the head main body 100 will be explained below. FIG. 2 shows aplan view illustrating the head main body 100. As shown in FIG. 2, thehead main body 100 has a flow passage unit 4 and the piezoelectric sheet(piezoelectric member) 21 which is formed on the upper surface of theflow passage unit 4. As shown in FIG. 2, the flow passage unit 4 has arectangular planar shape extending in one direction. A manifold 5, whichextends in parallel to the longitudinal direction of the flow passageunit 4, is formed in the flow passage unit 4. An ink supply port 100 ais formed at one end (left side end of the flow passage unit 4 as shownin FIG. 2) of the head main body 100. The ink supply port 100 a iscommunicated with the manifold 5. The ink supply port 100 a is connectedto an unillustrated ink tank via a tube or the like, and thus the ink issupplied from the ink tank to the manifold 5.

The piezoelectric sheet 21, which has a rectangular planar shape, isformed at an approximately central portion of the upper surface of theflow passage unit 4 with no interference with the ink supply port 100 a.A large number of pressure chambers (ink chambers) 10, which arearranged in the longitudinal direction of the flow passage unit 4, areformed in the flow passage unit 4 disposed opposingly to thepiezoelectric sheet 21. In other words, the piezoelectric sheet 21 hassuch a dimension that the piezoelectric sheet 21 ranges over all of thepressure chambers 10.

The pressure chamber 10, which is formed in the flow passage unit 4, hasa rectangular planar shape with its longitudinal direction beingparallel to the transverse direction of the flow passage unit 4. One endof the pressure chamber 10 is communicated with the nozzle 8, and theother end is communicated with the manifold 5. Accordingly, a largenumber of individual ink flow passages 7, which are formed for therespective pressure chambers 10 while being communicated with thenozzles 8, are connected to the manifold 5.

FIG. 3 shows a sectional view illustrating one of the individual inkflow passages, which is a partial sectional view taken along a lineIII-III shown in FIG. 2. As appreciated from FIG. 3, each of the nozzles8 is communicated with the manifold 5 via the pressure chamber 10. Thatis, one flow passage, which arrives at the nozzle 8 from the outlet ofthe manifold 5 via the pressure chamber 10, is constructed. In thismanner, the individual ink flow passage 7 is formed for each of thepressure chambers 10 in the head main body 100.

As shown in FIG. 3, the head main body 100 has a stacked structure inwhich six in total of sheet members, i.e., the uppermost piezoelectricsheet 21, an actuator plate (vibration plate) 22, a cavity plate 23, asupply plate 24, a manifold plate 25, and a nozzle plate 26 are stackedin this order. The flow passage unit 4 is constructed by five of theseplates except for the piezoelectric sheet 21.

A plurality of individual electrodes 35 are formed on the upper surfaceof the piezoelectric sheet 21 as described in detail later on. Thepiezoelectric sheet 21 has portions which serve as active sections to beopposed to the individual electrodes 35 when the driving voltage isapplied to the respective individual electrodes 35.

The actuator plate 22 is a metal plate which is provided with a hole toserve as the ink supply port 100 a. The cavity plate 23 is a metal platewhich is provided with a hole to serve as a communication hole from theink supply port 100 a to the manifold 5 and which is also provided witha large number of holes for constructing the pressure chambers 10, theholes being formed in areas opposed to the piezoelectric sheet 21. Thesupply plate 24 is a metal plate which is provided with a hole to serveas a communication hole from the ink supply port 100 a to the manifold 5and which is also provided with communication holes from the manifold 5to the pressure chambers 10 and communication holes from the pressurechambers 10 to the nozzles 8 respectively for each one of the pressurechambers 10 of the cavity plate 23. The manifold plate 25 is a metalplate which is provided with the manifold 5 and which is additionallyprovided with communication holes from the pressure chambers 10 to thenozzles 8 respectively for each one of the pressure chambers 10 of thecavity plate 23. The nozzle plate 26 is a resin plate which is providedwith the nozzles 8 respectively for each one of the pressure chambers 10of the cavity plate 23.

The five plates 22 to 26 are stacked while being positionally aligned toone another so that the individual ink flow passages 7 are formed asshown in FIG. 3. The individual ink flow passage 7 is firstly directedupwardly from the manifold 5, extends horizontally in the pressurechamber 10, and is directed vertically downwardly to the nozzle 8. Amongthe five plates for constructing the flow passage unit 4, the fourplates except for the nozzle plate 26 are composed of metal materialscomposed of stainless steel in this embodiment. However, they may becomposed of metal materials such as 42 Alloy and titanium. The reason,why the stainless steel is applied as the metal materials for therespective plates 22 to 25 in this embodiment, is as follows. That is,the coefficient of thermal expansion of 42 Alloy is approximate to thatof the piezoelectric sheet 21, and 42 Alloy is satisfactory in the fineetching processability. However, 42 Alloy is inferior in the corrosionresistance against the ink. On the other hand, the coefficient ofthermal expansion of titanium is small, and titanium is satisfactory inthe corrosion resistance against the ink. However, titanium isunsatisfactory in the fine etching processability. On the contrary,stainless steel is satisfactory in oxidation resistance, with which themechanical strength is lowered to a small extent even in the case of thehigh temperature processing. Stainless steel is satisfactory in the fineetching processability when the pressure chambers 10 or the like areformed. Stainless steel is not inferior in the fine etchingprocessability and the corrosion resistance as compared with 42 Alloyand titanium. The nozzle plate 26 is composed of polyimide resin.However, the nozzle plate 26 may be composed of any other resin materialor the same metal material as that of each of the other plates 22 to 25.

FIG. 4 shows a magnified view illustrating an area surrounded by dashedlines depicted in FIG. 3. As shown in FIG. 4, a surface layer 13 isformed on the entire upper surface of the actuator plate 22. Theactuator plate 22 and the piezoelectric sheet 21 are joined to eachother with the surface layer 13 intervening therebetween. In thisembodiment, the surface layer 13 includes a first buffer layer 14 whichis formed on the side of the actuator plate 22, and a second bufferlayer 15 which is formed on the side of the piezoelectric sheet 21. Bothof the first and second buffer layers 14, 15 are composed of metalmaterials which hardly cause the mutual diffusion with respect to thepiezoelectric sheet 21. The first buffer layer 14 is composed of nickelwhich hardly causes the mutual diffusion with respect to thepiezoelectric sheet 21 as compared with the stainless steel whichconstructs the actuator plate 22. The second buffer layer 15 is composedof gold which also hardly causes the mutual diffusion with respect tothe piezoelectric sheet 21 as compared with the stainless steel whichconstructs the actuator plate 22 in the same manner as the first bufferlayer 14.

In this manner, the actuator plate 22 and the piezoelectric sheet 21 arejoined to each other with the surface layer 13 intervening therebetweenby joining the actuator plate 22 to the first buffer layer 14, joiningthe first buffer layer 14 to the second buffer layer 15, and joining thepiezoelectric sheet 21 to the second buffer layer 15.

As shown in FIG. 2, the piezoelectric sheet 21 is a flat plate which isarranged to range over the large number of pressure chambers 10 of theflow passage unit 4. When the piezoelectric sheet 21 is arranged torange over the large number of pressure chambers 10, the individualelectrodes 35 can be arranged at a high density on the piezoelectricsheet 21 by using, for example, the screen printing technique.Therefore, the pressure chambers 10, which are formed at the positionscorresponding to the individual electrodes 35, can be also arranged at ahigh density. Thus, it is possible to print an image at a highresolution. In this embodiment, the piezoelectric sheet 21 is composedof a ceramic material based on the lead titanate zirconate (PZT) systemhaving ferroelectricity. However, the piezoelectric sheet 21 may becomposed of materials including, for example, those based on the leadmagnesium niobate (PMN) system, the lead nickel niobate (PNN) system,lead manganese niobate, lead antimony stannate, lead zinc niobate, andlead titanate.

Each one of the individual electrodes 35 is formed in the area opposedto each of the pressure chambers 10 on the upper surface of thepiezoelectric sheet 21. That is, the individual electrodes 35 arearranged in the longitudinal direction of the flow passage unit 4 in thesame manner as the pressure chambers 10. The individual electrodes 35are isolated from each other so that they are independent from oneanother. The individual electrodes 35 are composed of a metal materialsuch as Ag—Pd system, and they are electrically connected to independentwirings formed in FPC 20 respectively. Accordingly, the control unit cancontrol the electric potential for each of the pressure chambers 10 viathe wirings of the FPC 20. The actuator plate 22 is always maintained atthe ground electric potential, and it functions as a common electrode.

Next, a method for driving the actuator unit 21 will be described. Thepiezoelectric sheet 21 is polarized in the thickness direction thereof.Therefore, when an electric potential, which is higher than the groundelectric potential, is applied to the individual electrode 35, anelectric field is applied to the piezoelectric sheet 21 in the directionof polarization. When the electric field is applied to the piezoelectricsheet 21, the portion, to which the electric field is applied, acts asthe active layer which is elongated in the thickness direction and whichintends to contract in the surface direction in accordance with thelateral piezoelectric effect. Accordingly, the piezoelectric sheet 21and the actuator plate 22 are deformed to project toward the pressurechamber (unimorph deformation). In this situation, as shown in FIG. 3,the lower surface of the actuator plate 22 is fixed to the upper surfaceof the partition wall (cavity plate) 23 which comparts the pressurechamber 10. As a result, the piezoelectric sheet 21 and the actuatorplate 22 are deformed to project toward the pressure chamber. Therefore,the volume of the pressure chamber 10 is decreased, the pressure of theink is increased, and the ink is discharged from the nozzle 8. Afterthat, when the individual electrode 35 is returned to have the sameelectric potential as that of the actuator plate 22 which functions asthe common electrode, then the piezoelectric sheet 21 and the actuatorplate 22 are allowed to have the original shapes, and the volume of thepressure chamber 10 is returned to the original volume. Therefore, theink is sucked from the manifold 5.

Another driving method is also available as follows. That is, theindividual electrode 35 is previously allowed to have an electricpotential which is different from that of the actuator plate 22 whichserves as the common electrode. Every time when the discharge request ismade, then the individual electrode 35 is once allowed to have the sameelectric potential as that of the actuator plate 22, and then theindividual electrode 35 is allowed to have the electric potential whichis different from that of the actuator plate 22 again at a predeterminedtiming. In this procedure, the piezoelectric sheet 21 and the actuatorplate 22 are returned to have the original shapes at the timing at whichthe individual electrode 35 is allowed to have the same electricpotential as that of the actuator plate 22. Accordingly, the volume ofthe pressure chamber 10 is increased as compared with the initial state,and the ink is sucked from the manifold 5 into the pressure chamber 10.After that, the individual electrode is applied with a potential at atiming different from the timing when the actuator plate 22 is appliedwith the potential so that the piezoelectric sheet 21 and the actuatorplate 22 are deformed to project toward the pressure chamber 10. Thepressure of the ink is increased in accordance with the decrease in thevolume of the pressure chamber 10, and the ink is discharged. Thus, theink is discharged from the nozzles 8, and a desired image is printed onthe transported printing paper 41.

Next, an explanation will be made with reference to FIG. 5 about amethod for producing the ink-jet head 9 described above. FIG. 5 showssteps of producing the ink-jet head 9. FIG. 6 shows parts of the stepsof producing the ink-jet head 9 according to the embodiment of thepresent invention, wherein FIG. 6A shows a situation in which a stack isformed by the four plates except for the nozzle plate, FIG. 6B shows asituation in which the first buffer layer is formed on the upper surfaceof the actuator plate 22 and the second buffer layer is formed on thefirst buffer layer, FIG. 6C shows a situation in which the piezoelectricsheet is formed on the second buffer layer, and FIG. 6D shows asituation in which the individual electrode is formed on thepiezoelectric sheet.

When the ink-jet head 9 is produced, a stack 4 a, which is to form theflow passage unit 4 not including the nozzle plate 26, is firstlymanufactured in Step 1 (S1) as shown in FIG. 6A. In order to manufacturethe stack 4 a, the etching is applied by using masks of photoresistssubjected to the patterning on the respective plates 22 to 25 forconstructing the stack 4 a to form the holes as shown in FIG. 3 for therespective plates 22 to 25. The four plates 22 to 25, which arepositionally adjusted so that the individual ink flow passages 7 areformed, are pressed and heated in an overlapped state so that therespective plates 22 to 25 are joined to one another while effecting thediffusion.

Subsequently, in Step 2 (S2), the first buffer layer 14, which iscomposed of nickel, is formed by the electroplating method on the entireupper surface of the actuator plate 22 as shown in FIG. 6B. In Step 3(S3), as shown in FIG. 6B, the second buffer layer 15, which is composedof gold, is formed by the electroplating method on the entire uppersurface of the first buffer layer 14. Thus, the surface layer 13, whichis composed of the first and second buffer layers 14, 15, is formed. Inthis manner, it is possible to form, on the upper surface of theactuator plate 22, the surface layer 13 composed of nickel and gold inwhich the mutual diffusion hardly occurs to such an extent that thecrystal growth of the piezoelectric precursor layer (described later on)is inhibited, as compared with the stainless steel for constructing theactuator plate 22. Accordingly, the crystal growth of the piezoelectricprecursor layer is advanced without being inhibited in accordance withthe heating step as described later on, and it is possible to obtain thepiezoelectric sheet 21 which has the satisfactory piezoelectricperformance. In this embodiment, the electroplating method is used asthe method for forming the first and second buffer layers 14, 15.However, it is also allowable to apply any known method other than theabove, including, for example, the vapor growth method such as thesputtering and the vapor deposition, and the screen printing methodbased on the use of metal paste.

Subsequently, in Step 4 (S4), as shown in FIG. 6C, a piezoelectricmaterial paste is screen-printed to range over all of the pressurechambers 10 on the upper surface of the second buffer layer 15 to formthe piezoelectric precursor layer which is to be converted into thepiezoelectric sheet 21 having a thickness of about 20 μm. The stack,which is composed of the stack 4 a and the piezoelectric precursorlayer, is subjected to a degreasing treatment at 500° C. for 1 hour,followed by being subjected to a heating treatment at 850° C. for 10minutes to calcinate the piezoelectric precursor layer thereby.Accordingly, the piezoelectric precursor layer is converted into thepiezoelectric sheet 21 having a thickness of about 15 μm. In thisprocedure, it is preferable that a predetermined temperature in theheating step of heating the piezoelectric precursor layer is not lessthan 600° C. and not more than 900° C. If the predetermined temperatureis less than 600° C., then the crystal growth, which is caused by thecalcination of the piezoelectric precursor layer, becomes coarse, andthe piezoelectric performance of the piezoelectric sheet 21 isdeteriorated. On the other hand, if the predetermined temperatureexceeds 900° C., the strength is lowered, because the actuator plate 22is composed of the metal material (stainless steel). In other words,when the heating temperature for the piezoelectric precursor layer isnot less than 600° C. and not more than 900° C., then it is possible toavoid the inconveniences as described above, and it is possible tohardly cause the deterioration of the piezoelectric performance of thepiezoelectric sheet 21 and the decrease in the strength of the actuatorplate 22.

In this embodiment, the piezoelectric material paste is obtained bymixing, for example, a piezoelectric material powder based on the PZTsystem, minor components such as a sintering aid, ethyl cellulose as abinder, and terpineol as an organic solvent into a paste form. An easilysinterable material, which is capable of being sintered at a lowtemperature, is desirably used as the PZT-based piezoelectric materialpowder which serves as a base for the piezoelectric material paste, inorder to successfully use the actuator plate 22 made of metal. Thereactivity possessed by particles, i.e., the surface energy is inverselyproportional to the particle size or diameter, and the porosity, whichis obtained when the particles are packed most closely, is alsoinversely proportional to the particle size. Therefore, in thisembodiment, the particles are desirably to have small particle sizes,and the average particle size is not more than about 0.5 μm andpreferably not more than 0.2 μm. As described above, the piezoelectricmaterial powder based on the PZT system (i.e., the material for theformation as the base for the piezoelectric sheet 21) may be replaced,for example, with those based on the lead magnesium niobate system otherthan those based on the lead zirconate titanate system.

In this embodiment, the screen printing method is used to form thepiezoelectric precursor layer to be converted into the piezoelectricsheet 21. However, it is possible to apply other known methodsincluding, for example, the spin coating method, the dipping method, thecast method, the doctor blade method, the aerosol position method, thesol-gel method, and the organic compound pyrolysis method. Further, itis also possible to apply the transfer method. When the transfer methodis applied, a piezoelectric material paste, which is prepared in thesame manner as described above, is firstly used to prepare a green sheetfor which the thickness is managed, for example, by the doctor blademethod or the cast method. The green sheet is punched on a surface of aresin sheet having a high exfoliating property spread on a surface plateor the like, for example, by the press method to have a desired shape,and thus a piezoelectric precursor layer is formed. The piezoelectricprecursor layer is pressed while being positioned with respect to theupper surface of the actuator plate 22. Accordingly, the piezoelectricprecursor layer on the resin sheet can be transferred onto the actuatorplate 22.

Subsequently, in Step 5 (S5), as shown in FIG. 6D, a silver-basedconductive paste is screen-printed to form a pattern of the individualelectrodes 35 on the piezoelectric sheet 21, followed by being dried.After that, a stack, which is composed of the stack 4 a, thepiezoelectric sheet 21, and the silver-based conductive paste, is heatedand treated at 850° C. for 10 minutes. Thus, the silver-based conductivepaste is calcinated to form the individual electrodes 35 on thepiezoelectric sheet 21.

Subsequently, in Step 6 (S6), the nozzle plate 26 made of polyimideresin, through which the plurality of nozzles 8 are formed by the lasermachining, is adhered with an epoxy-based thermosetting adhesive to thelower surface of the stack which is composed of the stack 4 a, thepiezoelectric sheet 21, and the individual electrodes 35. Subsequently,in Step 7 (S7), the stack, to which the nozzle plate 26 has beenadhered, is pressed while being heated to a temperature of not less thanthe curing temperature of the thermosetting adhesive by using anunillustrated heating and pressing apparatus. In Step 8 (S8), the stack,which is taken out from the heating and pressing apparatus, is coolednaturally. Thus, the head main body 100, which is constructed by theflow passage unit 4 and the piezoelectric sheet 21, is produced.

After that, the ink-jet head 9 as described above is completed byperforming, for example, a step of joining the head main body 100 andthe base section 11. After that, a step of adhering FPC 20 and thepiezoelectric sheet 21 is performed, and then the ink-jet head 9 isfixed via the base section 11 to the frame 43 to which the paper feedmechanism, the paper discharge mechanism, and other components areassembled. Thus, the ink-jet printer 1 is produced.

According to the method for producing the ink-jet head 9 as describedabove, the surface layer 13 is allowed to intervene between thepiezoelectric sheet 21 and the actuator plate 22, and in the surfacelayer 13 the mutual diffusion is hardly caused to such an extent thatthe piezoelectric precursor layer, which is to be converted into thepiezoelectric sheet 21, is inhibited for the crystal growth, as comparedwith the actuator plate 22. Therefore, it is possible to avoid theoccurrence of any harmful influence which would be otherwise caused bythe mutual diffusion between the material for constructing thepiezoelectric precursor layer and the material for constructing theactuator plate 22 in the heating step of calcinating the piezoelectricprecursor layer to form the piezoelectric sheet 21. In other words, thefirst and second buffer layers 14, 15, which constitute the surfacelayer 13, are composed of nickel and gold, respectively, which scarcelyexert the harmful influence which would be otherwise caused by themutual diffusion between the piezoelectric precursor layer and the bothof nickel and gold, when the piezoelectric precursor layer, which is tobe converted into the piezoelectric sheet 21, is heated. Therefore, evenwhen the piezoelectric sheet 21 is calcinated on the actuator plate 22,the piezoelectric sheet 21 is obtained, in which the crystal growth ofthe piezoelectric precursor layer is advanced satisfactorily. As aresult, the deterioration of the performance of the piezoelectric sheet21 is hardly caused. The ink-jet head 9, which is produced as describedabove, has the piezoelectric sheet 21 in which the performance isscarcely deteriorated.

The second buffer layer 15 is formed on the first buffer layer 14.Therefore, the mutual diffusion is hardly caused between the materialfor constructing the piezoelectric precursor layer and the material forconstructing the actuator plate 22 in the heating step. Accordingly, anyharmful influence, which would be otherwise caused by the mutualdiffusion, is mitigated. The second buffer layer 15, which is composedof gold, is excellent in the thermal stability and the oxidationresistance. Therefore, it is possible to suppress the harmful influencewhich would be otherwise exerted by the mutual diffusion between thepiezoelectric precursor layer and the actuator plate 22. Further, anyoxide film is hardly formed at the interface between the surface layer13 and the piezoelectric sheet 21. Therefore, it is possible to apply asufficient electric field to the piezoelectric sheet 21 and the actuatorplate 22. The first buffer layer 14 is composed of cheap nickel.Therefore, it is possible to decrease the production cost of the ink-jethead.

EXAMPLES

Next, an explanation will be made below about Examples 1 to 9 in whichmetal materials for the surface layer 13 and metal materials for theactuator plate 22 are variously changed and combined. As shown in Table1, stacks are produced with combinations of surface layers 13 andactuator plates 22 in Examples 1 to 9. In this procedure, the stacks areproduced in accordance with approximately the same production method asthat for the ink-jet head 9 described above.

In Examples 1 to 4, the metal material for constructing the actuatorplate 22 is composed of stainless steel, and the thickness thereof is 20μm. The surface layer 13 of Example 1 is composed only of a nickel layerhaving a thickness of 5 μm. The surface layer 13 of Example 2 iscomposed of a nickel layer to serve as the first buffer layer 14 havinga thickness of 2 μm, and a gold layer to serve as the second bufferlayer 15 having a thickness of 0.2 μm. The surface layer 13 of Example 3is composed only of a gold layer having a thickness of 0.5 μm. Thesurface layer of Example 4 is composed of only a gold layer having athickness of 4 μm.

In Examples 5 to 7, the metal material for constructing the actuatorplate 22 is composed of 42 Alloy, and the thickness thereof is 20 μm.The surface layer 13 of Example 5 is composed only of a nickel layerhaving a thickness of 5 μm. The surface layer 13 of Example 6 iscomposed of a nickel layer to serve as the first buffer layer 14 havinga thickness of 2 μm, and a gold layer to serve as the second bufferlayer 15 having a thickness of 0.2 μm. The surface layer 13 of Example 7is composed only of a gold layer having a thickness of 4 μm.

In Examples 8 and 9, the metal material for constructing the actuatorplate 22 is composed of titanium, and the thickness thereof is 20 μm.The surface layer 13 of Example 8 is composed of a nickel layer to serveas the first buffer layer 14 having a thickness of 5 μm, and a goldlayer to serve as the second buffer layer 15 having a thickness of 0.2μm. The surface layer 13 of Example 9 is composed only of a platinumlayer having a thickness of 3 μm.

A piezoelectric sheet 21, which is composed of a ceramic material basedon the lead titanate zirconate system, is calcinated on the uppersurface of the stack formed by combining the actuator plate 22 and thesurface layer 13 of each of Examples, i.e., the upper surface of thesurface layer 13 to form a stack in which the actuator plate 22 and thepiezoelectric sheet 21 are joined to one another with the surface layer13 intervening therebetween for each of Examples 1 to 9. Table 1 showsthe evaluation about the piezoelectric performance and the crystalgrowth property of the piezoelectric sheet 21 of the stack, theoxidation resistance at the interface between the surface layer 13 andthe piezoelectric sheet 21, and the production cost of the head for eachof Examples obtained as described above. The crystal growth property wasevaluated based on an index determined as follows. That is, the surfaceof the piezoelectric sheet 21 after the calcination was observed with anelectron microscope having a 6,000× magnification to obtain a photographfor each of the combinations of the piezoelectric precursor layer andthe base material on which the piezoelectric precursor layer is to bestacked. Twenty crystal grains or particles were randomly selected inthe microscopic image of the piezoelectric sheet to measure particlesizes of the grains, and calculate the average value. The obtainedaverage value of particle size was used as the index. Alternatively,crystal growth property was evaluated based on the half band width (peakwidth at a half height) of X-ray diffraction peak. The oxidationresistance was evaluated by measuring the Tanδ of the piezoelectricsheet 21 for each of Examples and Comparative Examples.

On the other hand, a piezoelectric sheet, which is composed of a ceramicmaterial based on the lead titanate zirconate system, is sintered oneach of the actuator plates in which the metal materials forconstructing the actuator plates 22 are composed of stainless steel, 42Alloy, and titanium respectively to form stacks corresponding toComparative Examples 1 to 3. Table 1 also shows the evaluation about thepiezoelectric performance and the crystal growth property of thepiezoelectric sheet, the oxidation resistance at the interface betweenthe actuator plate and the piezoelectric sheet, and the production costof the head for each of the piezoelectric sheets of the stacks ofComparative Examples 1 to 3. The evaluations, which are expressed as“+”, “±”, and “−” in Table 1, are designated such that “+” is the bestevaluation, and “±” is the evaluation somewhat inferior to that of “+”.Further, “−” is the worst evaluation, indicating that any problemarises. TABLE 1 Crystal growth Surface layer property and First Secondpiezoelectric Oxidation Cost of Actuator plate buffer layer buffer layerperformance resistance head Example 1 stainless steel, nickel layer, — +± + t = 20 μm t = 5 μm Example 2 stainless steel, nickel layer, goldlayer, + + + t = 20 μm t = 2 μm t = 0.2 μm Example 3 stainless steel,gold layer, — ± + + t = 20 μm t = 0.5 μm Example 4 stainless steel, goldlayer, — + + − t = 20 μm t = 4 μm Example 5 42 Alloy, nickel layer, — +± + t = 20 μm t = 5 μm Example 6 42 Alloy, nickel layer, goldlayer, + + + t = 20 μm t = 2 μm t = 0.2 μm Example 7 42 Alloy, goldlayer, — + + − t = 20 μm t = 4 μm Example 8 titanium, nickel layer, goldlayer, + + + t = 20 μm t = 5 μm t = 0.2 μm Example 9 titanium, platinumlayer, — + + − t = 20 μm t = 3 μm Comp. Ex. 1 stainless steel, — — − + +t = 20 μm Comp. Ex. 2 42 Alloy, — — − ± + t = 20 μm Comp. Ex. 3titanium, — — − ± + t = 20 μm

As shown in Table 1, both of the crystal growth property and thepiezoelectric performance of the piezoelectric sheet are evaluated to be“−” in the case of the piezoelectric sheets of the stacks of ComparativeExamples 1 to 3, for the following reason. That is, iron, chromium andthe like, which are materials for constructing the actuator plate, aredisused into the piezoelectric sheet during the calcination of thepiezoelectric sheet, while lead, which constitutes the piezoelectricprecursor layer, is diffused into the actuator plate (mutual diffusion).Therefore, the crystal growth is inhibited for the piezoelectricprecursor layer to be converted into the piezoelectric sheet. As aresult, the piezoelectric performance of the piezoelectric sheet islowered in Comparative Examples 1 to 3. On the contrary, in the case ofthe piezoelectric sheets of the stacks of Examples 1 to 9, the surfacelayers 13, which are composed of the metal materials as shown in Table1, are formed between the actuator plates 22 and the piezoelectricsheets 21 respectively. Therefore, the component for constructing theactuator plate 22 and the component for constructing the piezoelectricprecursor layer to be converted into the piezoelectric sheet 21 asdescribed above are not subjected to the mutual diffusion during thecalcination of the piezoelectric sheet 21 to such an extent that thecrystal growth of the piezoelectric precursor layer is inhibited.Therefore, the piezoelectric performance of the piezoelectric sheet 21is not lowered, and hence the evaluation is “+” for almost all of themas shown in Table 1. Thus, the satisfactory results are obtained. Theevaluation is “±” for the crystal growth and the piezoelectricperformance of the piezoelectric sheet 21 in the case of only Example 3,for the following reason. That is, the thickness of the surface layer 13composed of the gold layer is extremely thin, i.e., 0.5 μm. Therefore,there is such a possibility that the material for constructing theactuator plate 22 may be incorporated into the piezoelectric sheet 21during the calcination of the piezoelectric sheet 21 in rare cases.However, the gold layer is formed as the surface layer 13 even when thelayer is thin. Therefore, even when the material for constructing theactuator plate 22 is incorporated into the piezoelectric sheet 21 duringthe calcination of the piezoelectric sheet 21, the amount thereof isextremely minute. Therefore, the crystal growth of the piezoelectricsheet 21 is scarcely inhibited. For this reason, the piezoelectricperformance of the piezoelectric sheet 21 is lowered extremely slightly.Therefore, the evaluation of “±” is given in Example 3.

In all of Comparative Examples 1 to 3, the production cost of the headare evaluated to be “+”. However, the oxidation resistance is evaluatedto be “±” in Comparative Examples 2 and 3, for the following reason.That is, 42 Alloy and titanium, which constitute the actuator plates ofComparative Examples 2 and 3, respectively, are slightly inferior in theoxidation resistance to stainless steel for constructing the actuatorplate of Comparative Example 1. On the contrary, the evaluation of theoxidation resistance is “+” for Examples 2 to 4 and Example 6 to 9 inwhich the layer, which forms the interface with respect to thepiezoelectric sheet 21, is gold or platinum layer, for the followingreason. That is, gold and platinum are excellent in the oxidationresistance than stainless steel. In Examples 1 and 5, the layer, whichforms the interface with respect to the piezoelectric sheet 21, is thenickel layer, and hence the evaluation of the oxidation resistance is“±”, for the following reason. That is, nickel is slightly inferior inthe oxidation resistance to stainless steel, gold, and platinum.However, even when the layer, which forms the interface with respect tothe piezoelectric sheet 21, is the nickel layer, nickel can be used asthe surface layer 13 without any problem, because the oxide film ishardly formed at the interface with respect to the piezoelectric sheet21.

In Examples 1 to 3, Example 5, and Examples 6 and 8, the gold orplatinum layer is not formed, or the thickness is extremely thin evenwhen the gold or platinum layer is formed. Therefore, the productioncost of the head is cheap, and the evaluation is “+”. However, inExamples 4, 7, and 9, the thickness of the gold or platinum layer islarge. Therefore, the price of the material for the gold or platinumlayer is expensive, and the evaluation is “−” in view of the productioncost of the head. The production cost of the head is of course cheap inComparative Examples 1 to 3, because the surface layer is not formed. InExamples 1 and 5, the surface layer 13 is formed only of the nickellayer, and nickel is extremely cheap. Therefore, the production cost ofthe head is the lowest in Examples 1 and 5 among Examples 1 to 9.

As described above, according to Examples 1 to 9, the crystal growth isadvanced satisfactorily during the calcination of the piezoelectricprecursor layer to be converted into the piezoelectric sheet 21, ascompared with Comparative Examples 1 to 3. Therefore, the piezoelectricperformance of the piezoelectric sheet 21 is scarcely deteriorated. Inother words, if the piezoelectric sheet is formed on the actuator platein the state in which no surface layer is formed as in ComparativeExamples 1 to 3, then the metal material for constructing the actuatorplate is incorporated therein during the calcination of thepiezoelectric precursor layer to be converted into the piezoelectricsheet, and the crystal growth of the piezoelectric precursor isinhibited. However, in the embodiments of the present invention, thevarious surface layers 13 are formed between the actuator plate 22 andthe piezoelectric sheet 21. Therefore, the crystal growth, which iseffected during the calcination of the piezoelectric precursor layer, isscarcely inhibited by the metal material for constructing the actuatorplate 22. Therefore, the piezoelectric performance of the piezoelectricsheet 21 is scarcely deteriorated. According to the above, it isappreciated that the deterioration of the piezoelectric performance ofthe piezoelectric sheet 21 is suppressed by forming, between theactuator plate 22 and the piezoelectric sheet 21, the surface layercomposed of the metal material which hardly causes the harmful influencethat would be otherwise caused by the mutual diffusion.

Next, Table 2 shows the influence exerted on the crystal growth propertyof the piezoelectric precursor layer by the difference in the quality ofthe base material (buffer layer intervening between the piezoelectricsheet and the actuator plate) for stacking the piezoelectric precursorlayer, with average values of particle size of the actuator sheet. Thebase materials, on which the piezoelectric precursor layer is to bestacked, are a nickel foil to be used in Example 10 and a gold foil tobe used in Example 11. On the other hand, stainless steel, which has thesame quality as that of the actuator plate, is used in ComparativeExample 4. A piezoelectric precursor layer, which is based on a rawmaterial of PZT-based piezoelectric particles having an average particlesize of 0.3 μm, was manufactured on each of the base materials. Afterthat, the piezoelectric precursor layer and each of the base materialswere heated at 850° C. for 15 minutes in an electric furnace, and thusthe piezoelectric precursor layer was subjected to the crystal growth.The average particle size of the piezoelectric sheet was measured foreach of Examples 10, 11 and Comparative Examples 4 in the same manner asexplained above. TABLE 2 Average particle size of Base materialpiezoelectric sheet Ex. 10 nickel foil 1.0 μm Ex. 11 gold foil 1.3 μmComp. Ex. 4 stainless steel 0.5 μm

According to Table 2, the growth is achieved in Example 10 such that theaverage particle size of the piezoelectric precursor layer convertedinto the piezoelectric sheet after the calcination arrives at theparticle size of 1 μm. In Example 11, the gold foil, which scarcelycauses the mutual diffusion and which has the high thermal stability, isused. Therefore, the piezoelectric precursor layer, which is convertedinto the piezoelectric sheet after the calcination, has the averageparticle size of 1.3 μm. In this result, the crystal growth of thepiezoelectric precursor layer is advanced as compared with Example 10.On the other hand, in Comparative Example 4, the piezoelectric sheet,which is converted into the piezoelectric sheet after the calcination,has the average particle size of 0.5 μm. Considering the fact that theaverage particle size of the piezoelectric precursor layer before thecalcination is 0.3 μm, the crystal growth of the piezoelectric precursorlayer converted into the piezoelectric sheet after the calcination isscarcely advanced in this result. Accordingly, it is appreciated thatthe calcinated piezoelectric precursor layer is subjected to the crystalgrowth satisfactorily while the crystal growth is not inhibited by thebase material, when the base material is the nickel foil as in Example10 or when the base material is the gold foil as in Example 11.

Preferred embodiments of the present invention have been explainedabove. However, the present invention is not limited to the embodimentsdescribed above, which can be variously changed and designed within ascope defined in claims. For example, magnesium, zinc, and niobium maybe used as metal materials other than nickel, in which the effect as thefirst buffer layer as explained above can be realized. In this case,those preferably usable as the method for forming the first buffer layerinclude the vapor growth method such as the sputtering method and thevapor deposition method. In the case of the ink-jet head 9 describedabove, the second buffer layer 15 is formed on the first buffer layer14. However, in view of the suppression of the mutual diffusion betweenthe actuator plate 22 and the piezoelectric sheet 21, the second bufferlayer 15 may not be provided when the first buffer layer 14 is composedof the metal material such as gold and platinum, for the followingreason. That is, gold and platinum have the excellent thermal stabilityand the excellent oxidation resistance. Therefore, it is possible tosuppress the mutual diffusion between the actuator plate 22 and thepiezoelectric sheet 21 and the formation of the oxide film to be formedat the interface with respect to the piezoelectric sheet 21 in the samemanner as in the embodiments described above. Further, the surface layermay be constructed only by the first buffer layer composed of nickel.Accordingly, it is possible to suppress the mutual diffusion between theactuator plate 22 and the piezoelectric sheet 21, although the oxidationresistance is inferior.

The second buffer layer 15 may be composed of a metal material otherthan gold and platinum. The actuator plate may be constructed by anymetal material other than stainless steel, 42 Alloy, and titaniumprovided that the metal material for constructing the actuator platedoes not cause the decrease in the strength even when the metal materialis heated at not less than the predetermined temperature.

The method for producing the ink-jet head 9 as described above may notinclude the step of forming the second buffer layer 15 provided that thelayer (first buffer layer), which serves as the surface layer, is formedbetween the actuator plate 22 and the piezoelectric sheet 21.

In the embodiments described above, the piezoelectric sheet(piezoelectric member) is formed to range over all of the pressurechambers. However, independent piezoelectric members corresponding tothe respective pressure chambers may be formed. In the embodimentsdescribed above, the plates except for the nozzle plate are integratedinto one unit by the joining while effecting the diffusion, and then thefirst and second buffer layers are formed on the actuator plate.However, an actuator plate, on which the buffer layers are previouslyprovided, may be used to form the flow passage unit by the joining whileeffecting the diffusion thereafter. The piezoelectric sheet ismanufactured after forming the flow passage unit by the joining whileeffecting the diffusion of the plates except of the nozzle plate.However, the following procedure may also be available. That is, thepiezoelectric sheet is formed for a stack in a state in which only theactuator plate is provided or the actuator plate and the cavity plateare joined to each other. Further, the remaining plates are stuckthereto with an adhesive to manufacture the flow passage unit.

1. A method for producing an ink-jet head, comprising the steps of:manufacturing a flow passage unit including a vibration plate which ismade of metal, an ink chamber which is closed by the vibration plate,and a nozzle which is communicated with the ink chamber and whichdischarges an ink; forming a first buffer layer on the vibration plate;forming a piezoelectric precursor on the first buffer layer; and heatingthe flow passage unit, the first buffer layer, and the piezoelectricprecursor so that the piezoelectric precursor is calcinated into apiezoelectric member, wherein: the first buffer layer is formed of ametal material with which mutual diffusion between the first bufferlayer and the piezoelectric precursor during the heating is less thanmutual diffusion between the piezoelectric precursor and the vibrationplate when the heating is performed without the first buffer layer. 2.The method for producing the ink-jet head according to claim 1, furthercomprising, before the heating step, a step of forming, on the firstbuffer layer, a second buffer layer formed of a metal material withwhich mutual diffusion between the second buffer layer and thepiezoelectric precursor during the heating is less than the mutualdiffusion between the vibration plate and the piezoelectric precursorwhen the heating is performed without the second buffer layer.
 3. Themethod for producing the ink-jet head according to claim 2, wherein thesecond buffer layer has oxidation resistance which is equivalent to orgreater than that of the vibration plate.
 4. The method for producingthe ink-jet head according to claim 1, wherein the vibration plate isformed of one material selected from the group consisting of stainlesssteel, titanium, and 42 Alloy, and the heating is performed in theheating step at a temperature of 600° C. to 900° C.
 5. The method forproducing the ink-jet head according to claim 1, wherein the firstbuffer layer is formed of one material selected from the groupconsisting of nickel, platinum, and gold.
 6. The method for producingthe ink-jet head according to claim 1, wherein the first buffer layer isformed of nickel.
 7. The method for producing the ink-jet head accordingto claim 3, wherein the second buffer layer is formed of gold.
 8. Themethod for producing the ink-jet head according to claim 1, wherein thefirst buffer layer has a thickness of not less than 2 μm.
 9. A methodfor producing an ink-jet head, comprising the steps of: manufacturing aflow passage unit including a vibration plate which is made of metal, anink chamber which is closed by the vibration plate, and a nozzle whichis communicated with the ink chamber and which discharges an ink;forming a nickel layer on the vibration plate; forming a gold layer onthe nickel layer; forming a piezoelectric precursor on the gold layer;and heating the flow passage unit, the nickel layer, the gold layer, andthe piezoelectric precursor at a temperature of 600° C. to 900° C. sothat the piezoelectric precursor is calcinated into a piezoelectricmember.
 10. The method for producing the ink-jet head according to claim9, wherein the vibration plate is formed of one material selected fromthe group consisting of stainless steel, titanium, and 42 Alloy.
 11. Anink-jet head comprising: a flow passage unit which includes a vibrationplate made of metal, an ink chamber closed by the vibration plate, and anozzle communicated with the ink chamber to discharge an ink; a firstbuffer layer which is formed on the vibration plate; and a piezoelectricmember which is formed on the first buffer layer and which is obtainedby calcinating a piezoelectric precursor, wherein: the first bufferlayer is formed of a metal material with which mutual diffusion betweenthe piezoelectric precursor and the first buffer layer during heatingfor the calcination is less than mutual diffusion between thepiezoelectric precursor and the vibration plate when the heating isperformed without the first buffer layer.
 12. The ink-jet head accordingto claim 11, further comprising a second buffer layer which is formedbetween the first buffer layer and the piezoelectric member and which isformed of a metal material with which mutual diffusion between thesecond buffer layer and the piezoelectric precursor during the heatingis less than the mutual diffusion between the vibration plate and thepiezoelectric precursor when the heating is performed without the secondbuffer layer.
 13. The ink-jet head according to claim 11, wherein thesecond buffer layer has oxidation resistance which is equivalent to orgreater than that of the vibration plate.
 14. The ink-jet head accordingto claim 11, wherein the vibration plate is formed of one materialselected from the group consisting of stainless steel, titanium, and 42Alloy.
 15. The ink-jet head according to claim 11, wherein the firstbuffer layer is formed of one material selected from the groupconsisting of nickel, platinum, and gold.
 16. The ink-jet head accordingto claim 12, wherein the second buffer layer is formed of gold.
 17. Theink-jet head according to claim 11, wherein the first buffer layer has athickness of not less than 2 μm.
 18. An ink-jet printer comprising theink-jet head as defined in claim 11.